In mineral mining installations it is well known to mount a drum-type cutting machine, such as a shearer, on a conveyor extending alongside a mineral, e.g. coal, face. The machine has a drive motor which rotates a toothed sprocket wheel which meshes with a stationary track, such as a chain, on the goaf side of the conveyor remote from the mineral face. As the sprocket wheel rotates the machine is driven back and forth above the conveyor to strip mineral from the mineral face with a rotating cutting drum and the conveyor then transports the mineral with a circulating scraper-chain assembly. To support and guide the machine a floor rail on the mineral face side of the conveyor supports running wheels whilst at the opposite goaf side the machine has vertically depending guide arms fitted with guide blocks which co-operate with guide projections slidably engaging in a guide rail supported on the conveyor. The guide blocks can clasp the guide rail substantially in the manner of a hook from above and/or below (see DE-PS 25 52 085, DE-PS 26 46 291, DE-OS 29 25 240).
In order to adapt the guide blocks to the course of the conveyor which is not normally horizontal, the guide blocks are mounted on the guide arms of the cutting machine so as to be pivotal in height to a limited extent by means of horizontal transverse bolts.
In order not only to provide compensation if the horizontal is not level, which is achieved by the pivotability of the guide block about a horizontal axis, but also to prevent jamming of the guide blocks when the conveyor does not extend exactly rectilinearly but adopts a curved course, for example if the individual conveyor pans snake, it is also already known additionally to make the guide blocks pivot around a vertical axis on the guide arm. Thus for this purpose the guide blocks according to DE-OS 196 33 491 are each provided with a vertical journal with which it is mounted so as to pivot rotatably to a limited extent in a journal socket on the guide arm. This known arrangement allows part rotation or pivoting of the guide block around a vertical as well as a horizontal axis in the manner of a universal joint so locking or clamping of the guide block and the guide rail can be substantially avoided. Nevertheless it has been found that, with the dimensions of the guide arm normally used, the forces occurring during cutting can barely be controlled with the known arrangement. Moreover, with a conventional material thickness of the guide arm of 120 mm and the necessary diameter of the vertical journal of 60 mm, there is a risk that the vertical bore on the guide arm will break out or deform and therefore will no longer be capable of holding the guide block with the necessary reliability.
A guide arrangement is known from DE-GM 68 02 117. In this arrangement a transverse bolt is held rigidly in the guide arm and tapers at the two outer ends projecting from the guide arm substantially frusto-conically to the ends. These frusto-conically converging portions of the transverse bolt are held in cylindrical bores in the guide block with ample play and, owing to their configuration, allow limited pivotability of the guide block relative to the guide arm of the cutting machine both vertically and horizontally. The disadvantage of this arrangement resides mainly in the fact that guide block and transverse bolt only make loose contact with one another in each direction and this results in enormously high wear of the components because the transverse bolt can only be applied after overcoming the play existing on the respectively opposed surface regions of the bores in the guide block during each change of direction of travel. A further disadvantage of this arrangement is that the guide block can move not only in the vertical direction and the desired horizontal direction transversely to the direction of travel of the cutting machine but also in a horizontal direction parallel to the direction of travel of the cutting machine. As a result, the guide projection can more easily become disengaged from the guide rail arranged on the conveyor and reliable guidance of the machine is no longer ensured.